/**
 * 牛客网.简单题.图片整理
 */

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Arrays;
import java.util.Scanner;

public class Main {
    //方法2 : 桶
    public static void main(String[] args) throws IOException {
        Scanner scanner = new Scanner(System.in);
        String string = scanner.nextLine();
        int[] ch = new int[128];
        for (int i = 0; i < string.length(); i++) {
            ch[string.charAt(i)]++;
        }
        for (int i = 0; i < 128; i++) {
            while(ch[i] != 0){
                System.out.print((char) i);
                ch[i]--;
            }
        }
    }

    //方法1
    public static void main1(String[] args) throws IOException {
        BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
        String s = new String(bf.readLine());
        char[] ch = s.toCharArray();
        Arrays.sort(ch);
        for (char x : ch) {
            System.out.print(x);
        }
    }
}